A typical disc drive includes one or more magnetic discs mounted for rotation on a hub or spindle. A typical disc drive also includes a transducer supported by a hydrodynamic air bearing which flies above each magnetic disc. The transducer and the hydrodynamic air bearing are collectively referred to as a data head. A drive controller is conventionally used for controlling the disc drive based on commands received from a host system. The drive controller controls the disc drive to retrieve information from the magnetic discs and to store information on the magnetic discs.
An electromechanical actuator operates within a negative feedback, closed-loop servo system. The actuator moves the data head radially over the disc surface for track seek operations and holds the transducer directly over a track on the disc surface for track following operations.
The spindle which supports the discs for rotation is driven by a spindle motor. The spindle is supported by bearings and typically has an annular flange thereabout. The discs are placed concentrically over the spindle, and are spaced apart axially along the spindle by annular spacer members.
Discs are conventionally fastened to the spindle using a shrinkable clamp member. Once the discs and spacers are assembled on the spindle, the clamp is heated and placed over the spindle and then allowed to cool and shrink such that it frictionally engages the outer periphery of the spindle to clamp the discs to the spindle. Prior to the clamping member becoming fixedly attached to the spindle, the discs are subjected to an axial preload force. Once the clamp becomes fixedly attached to the spindle, the preload force acts to fix the discs to the spindle for concentric rotation with the spindle.
In recent years, the storage capacity of discs has increased dramatically. One aspect of increasing the storage capacity is to increase the tracks per radial inch or tracks per inch (TPI) on the disc.
Runout (both repeatable and non-repeatable runout) associated with the bearing supporting the spindle can cause the discs supported by the spindle to wobble or exhibit displacement in the axial direction during rotation. In drives where the TPI is very high, this wobble or displacement can cause a disc to move relative to the data head by a distance which constitutes a large percent of a track width, or in some instances more than a track width. This can cause errors in writing data to the disc, or reading data from the disc.
The present invention provides a solution to this and other problems, and offers other advantages over the prior art.